The WikiLeaks founder also mumbled, paused and stuttered as he confirmed his name and date of birth at the beginning of the start of a case management hearing in London on Monday.
The American government is seeking to extradite the 48-year-old to prosecute him over the leak of hundreds of thousands of classified documents.
He faces 18 charges, including conspiracy to hack government computers and violation of espionage law, and could spend decades in prison if convicted.
Assange, who sported a long, unkempt beard when he was arrested in April, appeared clean-shaven and wore a dark blue suit over a pale blue sweater for the hearing at Westminster Magistrates’ Court.
John Pilger, the journalist and documentary filmmaker, and former mayor of London Ken Livingstone were among supporters seated in a packed public gallery as others protested outside court.
Mr Assange’s barrister, Mark Summers, described the extradition bid as “a political attempt” by Donald Trump’s administration to “signal to journalists the consequences of publishing information”.
“It is legally unprecedented,” he told the court.
Mr Summers said there was a “direct link” between Mr Trump’s election and the “reinvigoration” of the investigation, which had concluded under Barack Obama’s presidency without any charges against Mr Assange.
The barrister also claimed the US “has been actively engaged in intruding into privileged discussions between Assange and his lawyers” in the Ecuadorian embassy, where the WikiLeaks founder was holed up for nearly seven years after claiming asylum.
The intrusions included the “unlawful copying of their telephones and computers” and “hooded men breaking into offices,” Mr Summers alleged.
Such concerns were among “multiplicitous” issues which meant Assange’s legal team should be given more time to prepare for the case, argued the lawyer, who requested a three-month delay to the full extradition hearing.
But district judge Vanessa Baraitser refused to grant defence lawyers more time to gather evidence. She told Assange his next case management hearing would take place on 19 December and the full hearing would proceed as planned in February.
As court adjourned, Assange claimed he had not understood proceedings and complained: “This is not equitable.”
He added: “I can’t research anything, I can’t access any of my writing. It’s very difficult where I am.”
Assange, who is being held in high-security Belmarsh prison, told the judge he was up against a “superpower” with “unlimited resources” and appeared to be fighting back tears as he added: “I can’t think properly.”
He was jailed for 50 weeks in May for breaching his bail conditions by taking refuge in the Ecuadorian embassy in London to avoid extradition to Sweden over sex offence allegations.
Assange was arrested when police raided the embassy after the South American nation withdrew its offer of asylum.
He was due to be released from Belmarsh last month, but a judge remanded him in custody because there were “substantial grounds” for believing he would abscond.
Former home secretary Sajid Javid signed an order in June allowing the US extradition request to be heard in court.
In May, WikiLeaks claimed there were “grave concerns” about Assange’s health after he was moved to a medical ward in prison. When he did not appear for a scheduled court hearing, chief magistrate Emma Arbuthnot said the Australian was “not very well”.
WikiLeaks said at the time: “During the seven weeks in Belmarsh his health has continued to deteriorate and he has dramatically lost weight. The decision of the prison authorities to move him into the health ward speaks for itself.”
In a statement before the latest hearing on Monday, Amnesty International urged the UK to reject the extradition request.
Massimo Moratti, the human rights group’s deputy director for Europe, said: “The British authorities must acknowledge the real risks of serious human rights violations Julian Assange would face if sent to the USA.
“The UK must comply with the commitment it’s already made that he would not be sent anywhere he could face torture or other ill-treatment.”
Additional reporting by agencies